1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device that can suppress the movement of optical sheets by altering the structure of the sheets.
2. Description of the Conventional Art
Today, image displays have shifted from Braun tubes to liquid crystal displays, plasma display panels, etc. Especially, liquid crystal displays have attracted great attention as next-generation image displays because they have lower power consumption, are thinner and more lightweight, and emit much less undesirable electromagnetic radiation, compared to Braun tubes.
A liquid crystal display device comprises a lower substrate with TFTs (thin film transistors), an upper substrate with color filters arranged on it, and a liquid crystal layer injected between the lower substrate and the upper substrate.
The TFTs on the lower substrate serve to transmit and control electrical signals, and liquid crystals control the transmission of light by altering the molecular structure depending on an applied voltage. Light controlled by this process appears as an image of a desired color as it passes through the upper substrate.
Meanwhile, since the liquid crystal display device is a light receiving device that displays an image by adjusting the amount of light coming from the outside, it requires a separate light source, i.e., backlight assembly, for illuminating a liquid crystal panel.
The backlight assembly is roughly classified into an edge-lit backlight assembly and a direct-type backlight assembly depending on the position of the light source relative to a display surface. Especially, the edge-lit backlight assembly is widely used in large liquid crystal displays because it has high light utilization efficiency and is easy to handle and thin, with no limit on the size of the display surface.
A liquid crystal display device according to the related art which uses such an edge-lit backlight assembly will be described below with reference to FIGS. 1 to 5. The liquid crystal display device has a horizontal direction and a vertical direction when in an upright display orientation.
FIG. 1 is a top plan view schematically showing an optical sheet disposed on a light guide plate of a liquid crystal display device according to the related art.
FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1, which shows a combined cross-section of the liquid crystal display device according to the related art.
As shown in FIGS. 1 and 2, a liquid crystal display device according to the related art includes a liquid crystal panel 10 where an image is displayed, and a backlight unit 20 that is affixed to the liquid crystal panel 10 and provides light to the liquid crystal panel 10.
The liquid crystal panel 10 includes a color filter (CF) substrate 12, a thin film transistor substrate 14 provided under the color filter substrate 12, and a liquid crystal layer interposed between these substrates 12 and 14.
The backlight unit 20 includes a light guide plate 21, a light source array 23 disposed on one side of the light guide plate 21 and consisting of a plurality of light emitting elements 23a and an array substrate 23b, a group of optical sheets 22 disposed over the light guide plate 21, a reflective sheet 25 disposed under the light guide plate 21, a bottom cover 24 in which these components, i.e., the reflective sheet 25, the light guide plate 21, and the light source array 23, are contained, and a guide panel 26 that protects the bottom cover 24.
The liquid crystal panel 10 is seated and disposed on the guide panel 26.
The group of optical sheets 22 includes a diffusive sheet 22a that is stacked on the light guide plate 21 and diffuses light coming from the light guide plate 21, a plurality of prism sheets 22b that collect the light diffused by the diffusive sheet 22a and supply it uniformly across the entire area of the liquid crystal panel 10, and a top sheet implemented as a reflective polarizer 22c. 
FIG. 3 is an enlarged top plan view of the portion A of FIG. 1, which schematically shows a gap G1 between the light source array and the group of optical sheets and a vertical gap G2 between the bottom cover and the group of optical sheets when viewed in an upright display orientation.
FIG. 4 is an enlarged top plan view of the portion B of FIG. 1, which schematically shows a horizontal gap G3 between the bottom cover and the group of optical sheets when viewed in an upright display orientation.
FIG. 5 is an enlarged cross-sectional view of the portion C of FIG. 2, which schematically shows the gap G1 between the light source array and the group of optical sheets.
As shown in FIGS. 3 and 4, a first gap G1 is formed between the group of optical sheets 22 and the light source array 23, and second and third gaps G2 and G3 are formed vertically and horizontally, respectively, between the bottom cover 24 and the group of optical sheets 22 when viewed in an upright display orientation.
As such, as shown in FIG. 5, the liquid crystal display device according to the related art has no structure for fixing the group of optical sheets 22 vertically and horizontally. Thus, when the liquid crystal display device is shaken by hand, noise occurs due to movement of the group of optical sheets.
In the liquid crystal display device according to the related art, it is necessary to make gaps in order to assemble different components, for example, the bottom cover, the light source array, and the group of optical sheets. Moreover, in a high-temperature reliability test, the group of optical sheets expand thermally, and this increases the size of the group of optical sheets, thus causing interference with other components and resulting in wrinkles in the group of optical sheets.
To prevent these wrinkles in the group of optical sheets, it is necessary to make certain gaps between the group of optical sheets and other components in horizontal and vertical directions from the perspective of an upright display orientation.
Although these gaps between the components may prevent wrinkles in the group of optical sheets when assembling the group of optical sheets, they cannot prevent noise caused by the movement of the group of optical sheets when the liquid crystal display device is shaken by hand.
Accordingly, the group of optical sheets used in the liquid crystal display device according to the related art has its structural limitation when it comes to preventing noise caused by the movement of the group of optical sheets when the liquid crystal display device is shaken by hand.